Patients with low back pain are more likely to have surgery if they live in an area with more magnetic resonance imaging (MRI) machines, researchers say.

Action Points

Explain that patients living in areas with the highest concentrations of MRI machines were more likely to have an MRI if they complained of lower back pain, and were also more likely to have lower back surgery.

Note that the increase in surgery is cause for concern among researchers, since its efficacy has not been proven in the literature.

Patients with low back pain are more likely to have surgery if they live in an area with more magnetic resonance imaging (MRI) machines, researchers say.

In 2004, there would have been 5.4% fewer low back MRIs and 9% fewer back surgeries if all patients reporting new low back pain had been living in areas with the lowest availability of MRI machines, Jacqueline D. Baras, a medical student, and Laurence Baker, PhD, of Stanford University, reported online in Health Affairs.

Yet studies show increased surgery rates don't necessarily improve outcomes, as MRIs may also detect anomalies unrelated to back pain, they said.

"The worry is that many people will not benefit from the surgery, so heading in this direction is concerning," Baker said in a statement.

To examine the relationship between MRI availability and the use of MRI and surgery in patients with low back pain, the researchers collected data on Medicare patients who received care for low back pain from 1998 through 2005. They also analyzed data on the number of MRI machines in specific areas.

They found a total of 666,455 low back pain episodes, 15.6% of which resulted in a low back MRI and 2.7% of which resulted in lower back surgery within a year of the first visit.

Overall, increases in MRI availability were associated with increases in use of the technology for nonspecific low back pain, the researchers said.

For example, patients in areas with the highest quartile of MRI availability had a significant 1.09-fold increased likelihood of having an MRI for low back pain within a year of their initial visit, compared with those in areas with the lowest availability (95% CI 1.04 to 1.13).

In terms of predicted probability, those in the highest-quartile areas had a 17.2% chance of having an MRI during that time period, compared with a 15.8% chance for those in the lowest group.

The researchers said the study shows that low back pain patients are getting MRIs earlier in the course of their treatment, as two-thirds of scans happened within the first month of pain onset.

For example, the difference in probability between the highest and lowest quartiles of MRI availability is 1.1 percentage points at 30 days, but grows only to 1.4 percentage points at 365 days. That "suggests that most of the effect of MRI availability on low back MRI use becomes evident early in the course of treatment," the researchers said.

However, they noted that most guidelines recommend waiting until after one month for an MRI, because that's when most patients show spontaneous improvement.

The researchers calculated that if all Medicare patients with low back pain living in the second, third, and fourth quartiles of MRI availability in 2004 had instead lived in the lowest quartile, 12,277 fewer low back MRI scans would have been performed.

They also estimated that there would have been 3,521 fewer surgeries if all low back pain patients in those quartiles in 2004 had lived instead in areas with the lowest availability.

Patients in the highest quartile had a 1.23-fold increased likelihood of having surgery after a lower back MRI, compared with a 1.10-fold increased likelihood for those in the lowest.

Overall, that amounted to a 2.4-fold increased risk of surgery after an MRI for those living in areas with the highest availability of MRI, the researchers said.

Limitations of the study included use of claims data which did not record patient and physician preferences or patient health or outcome data, a short three-year time frame, and inclusion of Medicare patients only, which might limit generalizability.

Still, they concluded that "if increased MRI availability is associated with increased early use of low back MRI as well as with subsequent use of low back surgery, both of which have questionable clinical benefit, then widespread MRI diffusion may put patients at risk of a decrease in the quality of care they receive."

"We hope that this study will contribute to the debate over how to restrain the growth of healthcare spending without reducing access to high-quality care," they said.

The study was supported by grants from Stanford University School of Medicine and the California HealthCare Foundation.